An analysis of the membrane characteristics of the fluoropyrimidines (5'deoxy-5-fluorouridine, fluorodeoxyuridine, and fluorouracil), and methotrexate are being investigated. The characteristics of methotrexate transport is performed at extracellular concentrations relevant to drug levels achieved in high-dose methotrexate regimens in the presence and absence of vincristine. The role of fluoropyrimidines and methotrexate transport is being examined to aid in defining the proper sequence and interval between administration of these agents so that synergistic interactions are realized as a result of biochemical changes they produce.